rom/graphics/setmaxpen.c

   1 /*
   2     Copyright © 1995-2007, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Graphics function SetMaxPen()
   6     Lang: english
   7 */
   8 #include <graphics/rastport.h>
   9 #include "graphics_intern.h"
  10
  11 /*****************************************************************************
  12
  13     NAME */
  14 #include <proto/graphics.h>
  15
  16         AROS_LH2(void, SetMaxPen,
  17
  18 /*  SYNOPSIS */
  19         AROS_LHA(struct RastPort *, rp    , A0),
  20         AROS_LHA(ULONG            , maxpen, D0),
  21
  22 /*  LOCATION */
  23         struct GfxBase *, GfxBase, 165, Graphics)
  24
  25 /*  FUNCTION
  26         Set the maximum pen value for a rastport. This will instruct the
  27         graphics.library that the owner of the rastport will not be rendering
  28         in any colors whose index is >maxpen. Therefore speed optimizations
  29         on certain operations are possible and will be done.
  30
  31         Basically this call sets the rastport mask, if this would improve speed.
  32         On devices where masking would slow things down (chunky pixels), it will
  33         be a no-op.
  34
  35     INPUTS
  36         rp     = pointer to a valid RastPort structure
  37         maxpen = longword pen value
  38
  39     RESULT
  40
  41     NOTES
  42
  43     EXAMPLE
  44
  45     BUGS
  46
  47     SEE ALSO
  48         SetWriteMask()
  49
  50     INTERNALS
  51
  52     HISTORY
  53
  54 *****************************************************************************/
  55 {
  56   AROS_LIBFUNC_INIT
  57
  58   BYTE Mask;
  59
  60   /* maxpen==0 is nonsense */
  61   if (0 == maxpen)
  62     return;
  63
  64   /* calculate the Mask */
  65   /* maxpen   | Mask   | highest bit
  66    * 1        | 1      | 0
  67    * 2..3     | 3      | 1
  68    * 4..7     | 7      | 2
  69    * 8..15    | 15     | 3
  70    * 16..31   | 31     | 4
  71    * 31..63   | 63     | 5
  72    * 63..127  | 127    | 6
  73    * 128..255 | 255    | 7
  74    */
  75
  76   /* look for the highest bit */
  77   Mask = 0x0;
  78   while ((BYTE)maxpen != 0)
  79   {
  80     maxpen >>= 1;
  81     Mask = (Mask << 1) | 0x01;
  82   }
  83
  84   rp->Mask = Mask;
  85
  86   AROS_LIBFUNC_EXIT
  87 } /* SetMaxPen */